Aside from refraction (not a huge issue in flat planes of glass) the reflection of glass is other main thing.
Glass reflection is not uniform. Looking flat at it, it has fairly little reflection, maybe 10-20%. Seen on edge it is almost completely reflective, maybe 90%.
In A:M you can do this with a gradient combiner material, setting the first attribute to ~20% transparency and the other to ~90% and setting the "Edge Threshold" to 50%.
A very large or antique pane of glass with probably have some deviation from absolute flatness. "Roughness" can do that with the "Scale" set quite large.